The purpose of this research is to determine whether activity responsible for visually guided saccades or visually induced quick phases of nystagmus is transmitted through the mesencephalic reticular formation (MRF). We postulate that cells in this region produce activity that excites the paramedian zone of the pontine reticular formation (PPRF) to generate rapid eye movements. Trained monkeys watch spot of light that move unpredictably or are given full field movement to induce optokinetic nystagmus (OKN). Saccades made during ocular pursuit will also be studied. Eye movements are recorded with electrooculography (EOG), and will be registered with a scleral coil system. Extracellular unit activity in the MRF is correlated with parameters of on-target and off-target saccades, spontaneous saccades, and quick phases of OKN. The MRF is electrically stimulated to induce rapid eye movements and their characteristics are determined. Unit activity in the PPRF induced by MRF stimulation will also be studied. MRF lesions will be made and changes in saccades and quick phases and in PPRF unit activity will be determined after lesions. The PPRF will also be electrically stimulated after lesions during full field rotation to induce OKN. Afferent and efferent pathways to and from the MRF will be studied with horseradish peroxidase and radioactive amino acids to determine its inputs and outputs. These studies will localize portions of the MRF that are involved in oculomotor control. They will elucidate how activity that triggers visually-induced rapid eye movements is organized in this region, and determine how the MRF controls or affects the PPRF. They should provide information that would allow us to assess whether or not the MRF is a critical structure for production of visually-guided rapid eye movements.